U.S. patent application number 11/302824 was filed with the patent office on 2007-06-14 for stereoscopic display apparatus using lcd panel.
This patent application is currently assigned to Eastman Kodak Company. Invention is credited to Barry D. Silverstein.
Application Number | 20070132953 11/302824 |
Document ID | / |
Family ID | 37897335 |
Filed Date | 2007-06-14 |
United States Patent
Application |
20070132953 |
Kind Code |
A1 |
Silverstein; Barry D. |
June 14, 2007 |
Stereoscopic display apparatus using LCD panel
Abstract
A stereoscopic imaging apparatus (200) has an illumination
source (110) providing polarized illumination beams and at least
one uniformizing element (22) for uniformizing first and second
illumination beams. A left channel modulation apparatus (220l)
modulates the first polarized illumination beam to provide the left
eye portion of the stereoscopic image and a right channel
modulation apparatus (220r) modulates the second polarized
illumination beam to provide the right eye portion. Each channel
modulation apparatus has a color separator (78) for separating the
polarized illumination beam into at least a first component
wavelength illumination and a second component wavelength
illumination. Each channel modulation apparatus also has at least
two component wavelength modulating sections, each component
wavelength modulating section being a portion of a monochrome
transmissive liquid crystal modulator panel (60) that accepts a
corresponding component wavelength illumination and modulates the
component wavelength illumination to provide a modulated component
wavelength beam.
Inventors: |
Silverstein; Barry D.;
(Rochester, NY) |
Correspondence
Address: |
Mark G. Bocchetti;Patent Legal Staff
Eastman Kodak Company
343 State Street
Rochester
NY
14650-2201
US
|
Assignee: |
Eastman Kodak Company
|
Family ID: |
37897335 |
Appl. No.: |
11/302824 |
Filed: |
December 14, 2005 |
Current U.S.
Class: |
353/7 ;
348/E13.037; 348/E13.038; 348/E13.058 |
Current CPC
Class: |
H04N 13/337 20180501;
H04N 13/334 20180501; H04N 13/363 20180501 |
Class at
Publication: |
353/007 |
International
Class: |
G03B 21/00 20060101
G03B021/00 |
Claims
1. A stereoscopic imaging apparatus comprising: a) an illumination
source providing a first polarized illumination beam for a left eye
imaging channel and a second polarized illumination beam for a
right eye imaging channel, wherein the illumination source
comprises at least one uniformizing element for uniformizing the
first and second illumination beams; b) a left channel modulation
apparatus for modulating the first polarized illumination beam to
provide the left eye portion of a stereoscopic image and a right
channel modulation apparatus for modulating the second polarized
illumination beam to provide the right eye portion of the
stereoscopic image, wherein each channel modulation apparatus
further comprises: i) a color separator for separating the
polarized illumination beam into at least a first component
wavelength illumination and a second component wavelength
illumination; ii) at least two component wavelength modulating
sections, each component wavelength modulating section accepting a
corresponding component wavelength illumination and modulating the
component wavelength illumination to provide a modulated component
wavelength beam, each component wavelength modulating section
comprising: a portion of a monochrome transmissive liquid crystal
modulator panel that has been segmented into at least a first
portion and a second portion, and wherein each portion is spatially
separated from each other portion; an illumination path lens for
focusing the corresponding component wavelength illumination
through the corresponding portion of the monochrome transmissive
liquid crystal modulator panel; an analyzer for further
conditioning the polarization of the modulated component wavelength
beam; c) at least one projection lens for forming, onto a display
surface, a composite image that superimposes an image formed from
the modulated component wavelength beam of the left channel
modulation apparatus with the image formed from the modulated
component wavelength beam of the right channel modulation
apparatus; and d) a channel differentiator device provided to a
viewer for separating the left eye portion and right eye portion of
the stereoscopic image.
2. The projection apparatus according to claim 1 wherein the at
least two component wavelength modulating sections further comprise
a lens for forming the image formed from the modulated component
wavelength beam of the left channel modulation apparatus and the
image formed from the modulated component wavelength beam of the
right channel modulation apparatus as an intermediate image for
projection by the projection lens.
3. The projection apparatus according to claim 1 wherein the
illumination path lens is taken from a group consisting of a
Fresnel lens and a holographic lens.
4. The projection apparatus according to claim 1 wherein the
illumination source comprises a light source taken from a group
consisting of an LED, an LED array, a Xenon lamp, and a Mercury
lamp.
5. The projection apparatus according to claim 1 wherein the
uniformizing element comprises a lenslet array.
6. The projection apparatus according to claim 1 wherein the
uniformizing element comprises an integrating bar.
7. The projection apparatus according to claim 1 wherein the
transmissive liquid crystal modulator comprises thin film
transistors.
8. The projection apparatus according to claim 1 wherein the
transmissive liquid crystal modulator has a diagonal dimension of
at least five inches.
9. The projection apparatus according to claim 7 wherein the thin
film transistors are organic thin film transistors.
10. The projection apparatus according to claim 7 wherein the thin
film transistors comprise carbon nanotubes.
11. The projection apparatus according to claim 1 wherein at least
one component wavelength polarizer is spaced apart from the
monochrome transmissive liquid crystal modulator panel.
12. The projection apparatus according to claim 1 wherein the
polarizer is a wire grid polarizer.
13. The projection apparatus according to claim 12 wherein the wire
surface side of the wire grid polarizer device is oriented toward
the liquid crystal modulator panel.
14. The projection apparatus according to claim 1 wherein at least
one analyzer is a wire grid polarizer device.
15. The projection apparatus according to claim 14 wherein the wire
surface side of the wire grid polarizer device is oriented toward
the liquid crystal modulator panel.
16. The projection apparatus according to claim 1 wherein at least
one illumination path lens is a Fresnel lens spaced apart from the
monochrome transmissive liquid crystal modulator panel.
17. The projection apparatus according to claim 1 wherein at least
one illumination path lens is a holographic lens spaced apart from
the monochrome transmissive liquid crystal modulator panel.
18. The projection apparatus according to claim 1 further
comprising a) a sensor for detecting an offset in the superimposed
image between the image formed from the modulated component
wavelength beam of the left channel modulation apparatus and the
image formed from the modulated component wavelength beam of the
right channel modulation apparatus; and b) an imaging control
processor for shifting the position of at least one of the first or
second portions on the monochrome transmissive liquid crystal
modulator to compensate for the offset.
19. The projection apparatus according to claim 1 further
comprising a) a sensor for detecting an offset in the superimposed
image between the image formed from the modulated component
wavelength beam of the left channel modulation apparatus and the
image formed from the modulated component wavelength beam of the
right channel modulation apparatus; and b) an actuator coupled with
the at least one projection lens for adjusting lens position to
compensate for the offset.
20. The projection apparatus according to claim 19 wherein the
sensor information is used to improve the image resolution.
21. The projection apparatus according to claim 1 wherein at least
one of the component wavelength modulating sections further
comprises a modulated beam Fresnel lens.
22. The projection apparatus according to claim 1 wherein at least
one of the component wavelength modulating sections further
comprises a modulated beam holographic lens.
23. The projection apparatus according to claim 21 wherein the
modulated beam Fresnel lens is glass.
24. The projection apparatus according to claim 21 wherein the
modulated beam Fresnel lens comprises crossed cylindrical Fresnel
lenses.
25. The projection apparatus according to claim 1 wherein the
analyzer in at least one component wavelength modulating section
comprises a wire grid polarization beamsplitter.
26. The projection apparatus according to claim 1 wherein the
illumination source further comprises a shutter.
27. The projection apparatus according to claim 1 further
comprising a compensator.
28. The projection apparatus according to claim 27 wherein the
compensator is placed between the modulator panel and the at least
one component wavelength polarizer.
29. The projection apparatus according to claim 27 wherein the
compensator is a film-based component.
30. The projection apparatus according to claim 27 wherein the
compensator is a multi-dielectric thin film stack based
component.
31. The projection apparatus according to claim 27 wherein the
compensator is in the path of the first component wavelength
illumination.
32. The projection apparatus according to claim 27 wherein the
compensator is in the path of a modulated component wavelength
beam.
33. The projection apparatus according to claim 1 wherein the
analyzer is spaced apart from the liquid crystal modulator
panel.
34. The projection apparatus according to claim 1 wherein at least
one analyzer is a reflective polarizing beamsplitter.
35. The projection apparatus according to claim 27 wherein the
compensator comprises a formed birefringent structure.
36. The projection apparatus according to claim 1 wherein the first
and second component wavelength illumination are selected from the
group consisting of red, green, and blue illumination.
37. The projection apparatus according to claim 1 wherein the at
least two modulated component wavelength beams form an intermediate
image for projection by a projection lens.
38. The projection apparatus according to claim 1 wherein the
monochrome transmissive liquid crystal modulator panel has a first
antireflection coating on a first surface and a second
antireflection coating on a second surface.
39. The projection apparatus according to claim 1 further
comprising a color combiner to combine modulated component
wavelength beams for projection.
40. The projection apparatus according to claim 1 wherein the first
illumination beam is orthogonally polarized relative to the second
illumination beam.
41. The projection apparatus according to claim 1 wherein the first
illumination beam has a different spectral profile than the second
illumination beam.
42. The projection apparatus according to claim 1 wherein the
channel differentiator device separates the left and right eye
portions according to their respective transmissive spectral
profiles.
43. The projection apparatus according to claim 41 wherein the
spectral profile of the first illumination beam comprises red,
green, and blue wavelengths and the spectral profile of the second
illumination beam comprises yellow, magenta, and cyan spectral
profiles.
44. An imaging apparatus comprising: a) an illumination section
comprising: i) a light source providing a substantially unpolarized
illumination beam of multiple wavelengths; ii) a multiple
wavelength polarizer for polarizing the substantially unpolarized
illumination beam to provide a substantially polarized illumination
beam of multiple wavelengths; iii) a uniformizer for conditioning
the substantially polarized illumination beam of multiple
wavelengths to provide a uniformized polarized beam of multiple
wavelengths; iv) a color separator for separating the uniformized
polarized beam of multiple wavelengths into at least a first
component wavelength illumination and a second component wavelength
illumination; b) at least two component wavelength modulating
sections, each component wavelength modulating section accepting a
corresponding component wavelength illumination and modulating the
component wavelength illumination to provide a modulated component
wavelength beam, each component wavelength modulating section
comprising: i) a portion of a monochrome transmissive liquid
crystal modulator panel that has been segmented into at least a
first portion and a second portion, and wherein each portion is
spatially separated from each other portion; ii) a component
wavelength polarizer in the path of the component wavelength
illumination for directing substantially polarized light to the
corresponding portion of the monochrome transmissive liquid crystal
modulator panel; iii) an illumination path lens for focusing
incident illumination from the component wavelength polarizer
through the corresponding portion of the monochrome transmissive
liquid crystal modulator panel; iv) an analyzer for conditioning
the polarization of the modulated component wavelength beam; v) an
actuator coupled to the monochrome transmissive liquid crystal
light modulator for providing a dither movement; and, vi) a lens
for forming an image for projection onto a display surface; whereby
the image formed on the display surface comprises a plurality of
superimposed component wavelength beams.
45. The imaging apparatus according to claim 44 wherein the
illumination path lens is a Fresnel lens.
46. The imaging apparatus according to claim 44 wherein the
illumination path lens is a holographic lens.
47. An imaging apparatus comprising: a) an illumination section
comprising: i) a light source providing a substantially unpolarized
illumination beam of multiple wavelengths; ii) a multiple
wavelength polarizer for polarizing the substantially unpolarized
illumination beam to provide a substantially polarized illumination
beam of multiple wavelengths; iii) a uniformizer for conditioning
the substantially polarized illumination beam of multiple
wavelengths to provide a uniformized polarized beam of multiple
wavelengths; iv) a color separator for separating the uniformized
polarized beam of multiple wavelengths into at least a first
component wavelength illumination and a second component wavelength
illumination; b) at least two component wavelength modulating
sections, each component wavelength modulating section accepting a
corresponding component wavelength illumination and modulating the
component wavelength illumination to provide a modulated component
wavelength beam, each component wavelength modulating section
comprising: i) a portion of a monochrome transmissive liquid
crystal modulator panel that has been segmented into at least a
first portion and a second portion, and wherein each portion is
spatially separated from each other portion; ii) an illumination
path lens for focusing incident illumination from the component
wavelength polarizer through the corresponding portion of the
monochrome transmissive liquid crystal modulator panel; iii) a blur
filter provided in the path of at least one modulated component
wavelength beam; and iv) a lens for forming an image for projection
onto a display surface; whereby the image formed on the display
surface comprises a plurality of superimposed component wavelength
beams.
48. The imaging apparatus of claim 47 wherein at least one of the
component wavelength modulating sections further comprises: i) a
component wavelength polarizer in the path of the component
wavelength illumination for directing substantially polarized light
to the corresponding portion of the monochrome transmissive liquid
crystal modulator panel; and ii) an analyzer for conditioning the
polarization of the modulated component wavelength beam.
49. An imaging apparatus comprising: a) an illumination section
providing a first uniformized, polarized illumination beam of
multiple wavelengths and a second uniformized, polarized
illumination beam of multiple wavelengths; b) a first component
wavelength modulating section for modulating the first uniformized,
polarized illumination beam of multiple wavelengths and a second
component wavelength modulating section for modulating the second
uniformized, polarized illumination beam of multiple wavelengths,
each component wavelength modulating section comprising: i) a color
separator for separating the corresponding uniformized, polarized
beam of multiple wavelengths into at least a first component
wavelength illumination and a second component wavelength
illumination; ii) at least a portion of a monochrome transmissive
liquid crystal modulator panel for forming a modulated beam from an
incident light; iii) an illumination path lens for directing at
least the first and second component wavelength illumination to the
portion of the monochrome transmissive liquid crystal modulator
panel as the incident light; iv) a lens for directing the modulated
beam from the monochrome transmissive liquid crystal modulator
panel toward at least one projection lens; whereby the at least one
projection lens forms an image on a display surface.
50. The imaging apparatus of claim 49 wherein at least one of the
first and second component wavelength modulating sections further
comprise a dithering actuator for increasing the resolution of the
image formed on the display surface.
51. A method for forming an image on a display surface comprising:
a) providing a first uniformized, polarized illumination beam of
multiple wavelengths and a second uniformized, polarized
illumination beam of multiple wavelengths; b) modulating the first
uniformized, polarized illumination beam of multiple wavelengths at
a first component wavelength modulating section and modulating the
second uniformized, polarized illumination beam of multiple
wavelengths at a second component wavelength modulating section,
each component wavelength modulating section comprising: i) a color
separator for separating the corresponding uniformized, polarized
beam of multiple wavelengths into at least a first component
wavelength illumination and a second component wavelength
illumination; ii) at least a portion of a monochrome transmissive
liquid crystal modulator panel for forming a modulated beam from an
incident light; iii) an illumination path lens for directing at
least the first and second component wavelength illumination to the
portion of the monochrome transmissive liquid crystal modulator
panel as the incident light; iv) a lens for directing the modulated
beam from the monochrome transmissive liquid crystal modulator
panel toward at least one projection lens; and c) forming an image
from the modulated beams from the first and second component
wavelength modulating sections on a display surface.
52. A stereoscopic imaging apparatus comprising: a) an illumination
source providing a uniformized, polarized illumination beam; b) a
color scrolling element for conditioning the uniformized, polarized
illumination beam to provide a repeating sequence of at least two
color illumination beams; c) a transmissive spatial light modulator
for modulating the at least two color illumination beams to provide
corresponding modulated color beams; d) a switchable polarization
rotator in the path of the modulated color beams for repeatedly
switching the orientation of a polarization transmission axis
between two polarization states to provide the modulated color
beams in alternating polarization states; e) a projection lens for
directing the modulated color beams toward a display surface to
form a projected image having alternating polarization states; and
f) a channel differentiator device provided to a viewer for
separating the alternating polarization states to provide one
polarization state for viewing from the left eye and the other
polarization state for viewing from the right eye.
53. A stereoscopic imaging apparatus comprising: a) an illumination
source providing at least two uniformized, polarized color
illumination beams; b) a transmissive spatial light modulator for
modulating the at least two color illumination beams to provide
corresponding modulated color beams; c) a switchable polarization
rotator in the path of the modulated color beams for repeatedly
switching the orientation of a polarization transmission axis
between two polarization states to provide the modulated color
beams in alternating polarization states; d) a projection lens for
directing the modulated color beams toward a display surface to
form a projected image having alternating polarization states; and
e) a channel differentiator device provided to a viewer for
separating the alternating polarization states to provide one
polarization state for viewing from the left eye and the other
polarization state for viewing from the right eye.
54. A stereoscopic imaging apparatus comprising: a) an illumination
source providing a first illumination beam for a left eye imaging
channel and a second illumination beam for a right eye imaging
channel; b) a left channel modulation apparatus for modulating the
first illumination beam to provide the left eye portion of the
stereoscopic image and a right channel modulation apparatus for
modulating the second illumination beam to provide the right eye
portion of the stereoscopic image, wherein each channel modulation
apparatus further comprises: i) a uniformizing element for
conditioning the illumination beam to provide a uniformized beam;
ii) a color separator for separating the uniformized beam into at
least a first component wavelength illumination and a second
component wavelength illumination; iii) at least two component
wavelength modulating sections, each component wavelength
modulating section accepting a corresponding component wavelength
illumination and modulating the component wavelength illumination
to provide a modulated component wavelength beam, each component
wavelength modulating section comprising: a portion of a monochrome
transmissive liquid crystal modulator panel that has been segmented
into at least a first portion and a second portion, and wherein
each portion is spatially separated from each other portion; a
component wavelength polarizer in the path of the component
wavelength illumination for directing substantially polarized light
to the corresponding portion of the monochrome transmissive liquid
crystal modulator panel; an illumination path lens for focusing
incident illumination from the component wavelength polarizer
through the corresponding portion of the monochrome transmissive
liquid crystal modulator panel; an analyzer for conditioning the
polarization of the modulated component wavelength beam; and, a
lens for forming an intermediate image from modulated light; c) a
projection lens for forming, onto a display surface, a composite
image that superimposes the intermediate image formed by the left
channel modulation apparatus with the intermediate image formed by
the right channel modulation apparatus; and d) a channel
differentiator device provided to each viewer for separating the
left eye portion and right eye portion of the stereoscopic
image.
55. A method for displaying a stereoscopic image comprising: a)
providing a uniformized, polarized illumination beam; b)
conditioning the uniformized, polarized illumination beam to
provide a repeating sequence of at least two color illumination
beams; c) modulating the at least two color illumination beams to
provide corresponding modulated color beams; d) switching the
orientation of a polarization transmission axis repeatedly between
two polarization states to provide the modulated color beams in
alternating polarization states; e) directing the modulated color
beams toward a display surface to form a projected image having
alternating polarization states; and f) providing a channel
differentiator device to a viewer for separating the alternating
polarization states to provide one polarization state for viewing
from the left eye and the other polarization state for viewing from
the right eye.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application is related to pending U.S. patent
application Ser. No. 11/120,331, filed May 3, 2005, entitled
DISPLAY APPARATUS USING LCD PANEL, by Silverstein et al., the
disclosure of which is incorporated herein.
FIELD OF THE INVENTION
[0002] This invention generally relates to electronic projection
and more particularly relates to a stereoscopic electronic
projection apparatus using an LC modulator panel or panels for
forming a full color stereoscopic projection image.
BACKGROUND OF THE INVENTION
[0003] Liquid crystal (LC) technology has been successfully
harnessed to serve numerous display applications, ranging from
monochrome alphanumeric display panels, to laptop computers, and
even to large-scale full color displays. As is well known, an LC
device forms an image as an array of pixels by selectively
modulating the polarization state of incident light for each
corresponding pixel. Continuing improvements of LC technology have
yielded the benefits of lower cost, improved yields and
reliability, and reduced power consumption and with steadily
improved imaging characteristics, such as resolution, speed, and
color.
[0004] One type of LC display component, commonly used for laptops
and larger display devices, is the so-called "direct view" LCD
panel, in which a layer of liquid crystal is sandwiched between two
sheets of glass or other transparent material. Continuing
improvement in thin-film transistor (TFT) technology has proved
beneficial for direct view LCD panels, allowing increasingly denser
packing of transistors into an area of a single glass pane. In
addition, new LC materials that enable thinner layers and faster
response time have been developed. This, in turn, has helped to
provide direct view LCD panels having improved resolution and
increased speed. Thus, larger, faster LCD panels having improved
resolution and color are being designed and utilized successfully
for full motion imaging.
[0005] Alternatively, miniaturization and the utilization of
microlithographic technologies have enabled development of LC
devices of a different type. Liquid crystal on silicon (LCOS)
technology has enabled the development of highly dense spatial
light modulators by sealing the liquid crystal material against the
structured backplane of a silicon circuit. Essentially, LCOS
fabrication combines LC design techniques with complementary
metal-oxide semiconductor (CMOS) manufacturing processes.
[0006] Using LCOS technology, LC chips having imaging areas
typically smaller than one square inch are capable of forming
images having several million pixels. The relatively mature level
of silicon etching technology has proved to be advantageous for the
rapid development of LCOS devices exhibiting high speeds and
excellent resolution. LCOS devices have been used as spatial light
modulators in applications such as rear-projection television and
business projection apparatus.
[0007] With the advent of digital cinema and related electronic
imaging opportunities, considerable attention has been directed to
development of electronic projection apparatus. In order to provide
a competitive alternative to conventional cinematic-quality film
projectors, digital projection apparatus must meet high standards
of performance, providing high resolution, wide color gamut, high
brightness, and frame-sequential contrast ratios exceeding 1,000:1.
LCOS LCDs appear to have advantages as spatial light modulators for
high-quality digital cinema projection systems. These advantages
include relatively large device size, small gaps between pixels,
and favorable device yields.
[0008] Referring to FIG. 1, there is shown a simplified block
diagram of a conventional electronic projection apparatus 10 using
LCOS LCD devices. Each color path (r=Red, g=Green, b=Blue) uses
similar components for forming a modulated light beam. Individual
components within each path are labeled with an appended r, g, or
b, appropriately. Following the red color path, a red light source
20r provides unmodulated light, which is conditioned by
uniformizing element 22r to provide a uniform illumination. A
polarizing beamsplitter 24r directs light having the appropriate
polarization state to a spatial light modulator 30r which
selectively modulates the polarization state of the incident red
light over an array of pixel sites. The action of spatial light
modulator 30r forms the red component of a full color image. The
modulated light from this image, transmitted along an optical axis
O.sub.r through polarizing beamsplitter 24r, is directed to a
dichroic combiner 26, typically an X-cube or a Philips prism.
Dichroic combiner 26 combines the red, green, and blue modulated
images from separate optical axes O.sub.r/O.sub.g/O.sub.b to form a
combined, multicolor image for a projection lens 32 along a common
optical axis O for projection onto a display surface 40, such as a
projection screen. Optical paths for blue and green light
modulation are similar. Green light from green light source 20g,
conditioned by uniformizing element 22g is directed through a
polarizing beamsplitter 24g to a spatial light modulator 30g. The
modulated light from this image, transmitted along an optical axis
O.sub.g, is directed to dichroic combiner 26. Similarly blue light
from red light source 20b, conditioned by uniformizing optics 22b
is directed through a polarizing beamsplitter 24b to a spatial
light modulator 30b. The modulated light from this image,
transmitted along an optical axis O.sub.b, is directed to dichroic
combiner 26.
[0009] Among examples of electronic projection apparatus that
utilize LCOS LCD spatial light modulators with an arrangement
similar to that of FIG. 1 are those disclosed in U.S. Pat. No.
5,808,795 (Shimomura et al.); U.S. Pat. No. 5,798,819 (Hattori et
al.); U.S. Pat. No. 5,918,961 (Ueda); U.S. Pat. No. 6,010,221 (Maki
et al.); U.S. Pat. No. 6,062,694 (Oikawa et al.); U.S. Pat. No.
6,113,239 (Sampsell et al.); and U.S. Pat. No. 6,231,192 (Konno et
al.)
[0010] As each of the above-cited patents shows, developers of
motion-picture quality projection apparatus have primarily directed
their attention and energies to LCOS LCD technology, rather than to
solutions using TFT-based, direct view LC panels. There are a
number of clearly obvious reasons for this. For example, the
requirement for making projection apparatus as compact as possible
argues for the deployment of miniaturized components, including
miniaturized spatial light modulators, such as the LCOS LCDs or
other types of compact devices such as digital micromirrors. The
highly compact pixel arrangement, with pixels typically sized in
the 10-20 micron range, allows a single LCOS LCD to provide
sufficient resolution for a large projection screen, requiring an
image in the range of 2048.times.1024 or 4096.times.2048 pixels or
better as required by Society of Motion Picture and Television
Engineers (SMPTE) specifications for digital cinema projection.
Other reasons for interest in LCOS LCDs over their direct-view LCD
panel counterparts relates to performance attributes of currently
available LCOS components, attributes such as response speed,
color, and contrast.
[0011] Yet another factor that tends to bias projector development
efforts toward miniaturized devices relates to the dimensional
characteristics of the film that is to be replaced. That is, the
image-forming area of the LCOS LCD spatial light modulator, or its
digital micromirror device (DMD) counterpart, is comparable in size
to the area of the image frame that is projected from the motion
picture print film. This may somewhat simplify some of the
projection optics design. However, this interest in LCOS LCD or DMD
devices also results from an unquestioned assumption on the part of
designers that image formation at smaller dimensions is most
favorable. Thus, for conscious reasons, and in line with
conventional reasoning and expectations, developers have assumed
that the miniaturized LCOS LCD or DMD provides the most viable
image-forming component for high-quality digital cinema
projection.
[0012] One problem inherent with the use of miniaturized LCOS and
DMD spatial light modulators relates to brightness and efficiency.
As is well known to those skilled in the imaging arts, any optical
system is constrained by the Lagrange invariant. A product of the
area of the light-emitting device and the numerical aperture of the
emitted light, the LaGrange invariant is an important consideration
for matching the output of one optical system with the input of
another and determines output brightness of an optical system. In
simple terms, only so much light can be provided from an area of a
certain size. As the Lagrange invariant shows, when the emissive
area is small, a large angle of emitted light is needed in order to
achieve a certain level of brightness. Added complexity and cost
result from the requirement to handle illumination at larger
angles. This problem is noted and addressed in commonly assigned
U.S. Pat. No. 6,758,565 (Cobb et al.); U.S. Pat. No. 6,808,269
(Cobb); and U.S. Pat. No. 6,676,260 (Cobb et al.) These patents
disclose electronic projection apparatus design using higher
numerical apertures at the spatial light modulator for obtaining
the necessary light while reducing angular requirements elsewhere
in the system.
[0013] A related consideration is that image-forming components
also have limitations on energy density. With miniaturized spatial
light modulators, and with LCOS LCDs in particular, only so much
energy density can be tolerated at the component level. That is, a
level of brightness beyond a certain threshold level can damage the
device itself. Typically, energy density above about 15 W/cm.sup.2
would be excessive for an LCOS LCD. This, in turn, constrains the
available brightness when using an LCOS LCD of 1.3 inch in diameter
to no more than about 15,000 lumens. Heat build-up must also be
prevented, since this would cause distortion of the image, color
aberrations, and could shorten the lifespan of the light modulator
and its support components. In particular, the behavior of the
absorptive polarization components used can be significantly
compromised by heat build-up. This requires substantial cooling
mechanisms for the spatial light modulator itself and careful
engineering considerations for supporting optical components.
Again, this adds cost and complexity to optical system design.
[0014] Still other related problems with LCOS LCDs relate to the
high angles of modulated light needed. The mechanism for image
formation in LCD devices and the inherent birefringence of the LCD
itself limit the contrast and color quality available from these
devices when incident illumination is highly angular. In order to
provide suitable levels of contrast, one or more compensator
devices must be used in an LCOS system. This, however, further
increases the complexity and cost of the projection system. An
example of this is disclosed in commonly assigned U.S. Pat. No.
6,831,722 (Ishikawa et al.), which discloses the use of
compensators for angular polarization effects of wire grid
polarizers and LCD devices. For these reasons, it can be
appreciated that LCOS LCD and DMD solutions face inherent
limitations related to component size and light path geometry.
[0015] There have been various projection apparatus solutions
proposed using the alternative direct view TFT LC panels. However,
in a number of cases, these apparatus have been proposed for
specialized applications, and are not intended for use in high-end
digital cinema applications. For example, U.S. Pat. No. 5,889,614
(Cobben et al.) discloses the use of a TFT LC panel device as an
image source for an overhead projection apparatus. U.S. Pat. No.
6,637,888 (Haven) discloses a rear screen TV display using a single
subdivided TFT LC panel with red, green, and blue color sources,
using separate projection optics for each color path. Commonly
assigned U.S. Pat. No. 6,505,940 (Gotham et al.) discloses a
low-cost digital projector with a large-panel LC device encased in
a kiosk arrangement to reduce vertical space requirements. While
each of these examples employs a larger LC panel for image
modulation, none of these designs is intended for motion picture
projection at high resolution, having good brightness levels, color
comparable to that of conventional motion picture film, acceptable
contrast, and a high level of overall image quality.
[0016] One attempt to provide a projection apparatus using TFT LC
panels is disclosed in U.S. Pat. No. 5,758,940 (Ogino et al.) In
the Ogino et al. '940 apparatus, one or more Fresnel lenses is used
to provide collimated illumination to the LC panel; another Fresnel
lens then acts as a condenser to provide light to projection
optics. Because it provides an imaging beam over a wide area, the
Ogino et al. '940 apparatus has a high light output, based on the
Lagrange invariant described above. However, while it offers
potential applications for TV projection apparatus and small-scale
projectors, the proposed solution of the Ogino et al. '940
disclosure falls short of the performance levels necessary for
high-resolution projection systems that modulate light and provide
imaged light output having high intensity, at levels of 10,000
lumens and beyond.
[0017] Thus, it can be seen that, although digital cinema
projection apparatus solutions have focused on the use of LCOS LCDs
for image forming, there are inherent limitations in brightness and
efficiency when using LCOS LCD components for this purpose. TFT LC
panel solutions, meanwhile, would provide enhanced brightness
levels over LCOS solutions. While projection apparatus using TFT LC
panels have been disclosed, these have not been well suited to the
demanding brightness requirements of high-performance digital
cinema projection.
[0018] In cinema applications, the projector projects the modulated
image onto a display screen or surface, which may be at a variable
distance from the projector. This requires that the projector
provide some type of focus adjustment as well as color alignment
adjustment. With conventional LCOS apparatus such as that shown in
FIG. 1, color alignment is performed by color combining optics, so
that the three composite RGB colors are projected along the same
axis. However, for solutions using TFT devices, there would be
benefits to providing separate projection optics for red, green,
and blue paths. Some of these benefits include simpler and less
costly lenses with color correction for a narrow wavelength band at
each lens. With such an approach, some alignment method must then
be provided to form the color image from properly superimposed red,
green, and blue images, thereby allowing the projector to be used
over a range of distances from a display screen.
[0019] Other problems relate to the nature of light modulation by
the TFT LC device and to the support components necessary for high
brightness applications requiring high levels of image quality.
Conventional solutions would constrain both the light output levels
and overall image quality, obviating the advantages afforded by TFT
use for projection applications. For example, the use of absorptive
polarizers directly attached to the TFT panels, as these devices
are commonly provided, is disadvantageous for image quality. Heat
absorption from these films, typically exceeding 20% of the light
energy, causes consequent heating of the LCD materials, resulting
in a loss of contrast and contrast uniformity.
[0020] Stereoscopic or "3D" imaging techniques have been used to
provide improved visual depth for projected images. In conventional
stereoscopic projection, two overlapping images are projected onto
a display surface, with each image having different optical
properties. In stereoscopic imaging systems that use polarization
to differentiate left and right images, there is one image at one
polarization for the right eye, one image at an orthogonal
polarization for the left. The viewer is provided with a pair of
polarized goggles or glasses, with the left and right portions
differing with respect to the orientation of the polarization axis.
For example, the light projected for the left eye image may be
s-polarized and the light for the right eye image p-polarized.
Other stereoscopic systems may use color to differentiate left-eye
from right-eye images, with corresponding color-selective filters
in viewing glasses.
[0021] Conventional stereoscopic imaging systems using electronic
display components are typically inefficient and provide low
brightness levels. Thus, it can be appreciated that there would be
advantages to a full-color stereoscopic projection apparatus that
takes advantage of inherent Lagrange-invariant-related advantages
of TFT LC devices and provides improved image quality.
SUMMARY OF THE INVENTION
[0022] Briefly, according to one aspect of the present invention to
provide a stereoscopic imaging apparatus having: [0023] a) an
illumination source providing a first polarized illumination beam
for a left eye imaging channel and a second polarized illumination
beam for a right eye imaging channel, wherein the illumination
source comprises at least one uniformizing element for uniformizing
the first and second illumination beams; [0024] b) a left channel
modulation apparatus for modulating the first polarized
illumination beam to provide the left eye portion of the
stereoscopic image and a right channel modulation apparatus for
modulating the second polarized illumination beam to provide the
right eye portion of the stereoscopic image, wherein each channel
modulation apparatus further comprises: [0025] i) a color separator
for separating the polarized illumination beam into at least a
first component wavelength illumination and a second component
wavelength illumination; [0026] ii) at least two component
wavelength modulating sections, each component wavelength
modulating section accepting a corresponding component wavelength
illumination and modulating the component wavelength illumination
to provide a modulated component wavelength beam, each component
wavelength modulating section comprising: [0027] a portion of a
monochrome transmissive liquid crystal modulator panel that has
been segmented into at least a first portion and a second portion,
and wherein each portion is spatially separated from each other
portion; [0028] an illumination path lens for focusing the
corresponding component wavelength illumination through the
corresponding portion of the monochrome transmissive liquid crystal
modulator panel; [0029] an analyzer for further conditioning the
polarization of the modulated component wavelength beam; [0030] c)
at least one projection lens for forming, onto a display surface, a
composite image that superimposes an image formed from the
modulated component wavelength beam of the left channel modulation
apparatus with the image formed from the modulated component
wavelength beam of the right channel modulation apparatus; and
[0031] d) a channel differentiator device provided to a viewer for
separating the left eye portion and right eye portion of the
stereoscopic image.
[0032] It is a feature of the present invention that, unlike
current approaches that use miniaturized LCOS LCDs, the apparatus
of the present invention employs one or more LCD panels for
stereoscopic imaging in a projection apparatus intended for
high-end electronic imaging applications.
[0033] It is an advantage of the present invention that it allows
added brightness for the projected stereoscopic image. Various
types of light sources could be used.
[0034] These and other objects, features, and advantages of the
present invention will become apparent to those skilled in the art
upon a reading of the following detailed description when taken in
conjunction with the drawings wherein there is shown and described
an illustrative embodiment of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter of the
present invention, it is believed that the invention will be better
understood from the following description when taken in conjunction
with the accompanying drawings, wherein:
[0036] FIG. 1 is a block diagram showing a conventional projection
apparatus using LCOS LCD devices;
[0037] FIG. 2 is a block diagram of a stereoscopic imaging
apparatus according to the present invention;
[0038] FIG. 3 is a block diagram showing a polarized light
providing apparatus;
[0039] FIG. 4 is a block diagram showing a left- or right-channel
modulation apparatus;
[0040] FIG. 5 is a plan view of a TFT LC device segmented according
to the present invention, subdivided into component color
modulating sections;
[0041] FIG. 6A is a cross section of a conventional large panel LC
device;
[0042] FIG. 6B is a cross section of a simplified large panel LC
device according to the present invention;
[0043] FIG. 7 is a perspective view of a projection apparatus
according to the present invention;
[0044] FIG. 8 is a block diagram showing a color separator in one
embodiment;
[0045] FIG. 9 is a block diagram showing a projection apparatus
with a control loop for alignment;
[0046] FIG. 10 is a block diagram of an embodiment using multiple
light sources and two Fresnel lenses in each color channel;
[0047] FIG. 11 is a schematic block diagram showing an alternate
embodiment using color scrolling in a two panel apparatus;
[0048] FIG. 12 is a schematic diagram, in perspective, showing an
alternate embodiment using a polarization beamsplitter in each
color channel;
[0049] FIG. 13 is a schematic block diagram showing an alternate
embodiment of a portion of a color projection apparatus using a
V-prism as color combiner for modulated light;
[0050] FIG. 14 is a schematic block diagram showing an embodiment
using dither to enhance pixel fill factor;
[0051] FIG. 15 is a schematic block diagram showing the an
embodiment using a blur filter to enhance pixel fill factor;
and
[0052] FIG. 16 is a schematic block diagram of an imaging apparatus
in an alternate embodiment showing a switchable polarization
rotating element.
DETAILED DESCRIPTION OF THE INVENTION
[0053] The present description is directed in particular to
elements forming part of, or cooperating more directly with,
apparatus in accordance with the invention. It is to be understood
that elements not specifically shown or described may take various
forms well known to those skilled in the art.
[0054] The present invention adapts one or more TFT LC devices for
use in stereoscopic projection. The major components of a
stereoscopic imaging apparatus 200 are shown in the block diagram
of FIG. 2. An illumination source 210 splits light, according to a
characteristic property such as polarization or spectral content,
into two channels, a left channel and a right channel. Each channel
is provided for modulation: the left channel to a modulation
apparatus 220l and the right channel to a modulation apparatus
220r. Modulation apparatus 220l and 220r operate to form an image
64, such as an intermediate image as shown in FIG. 2, that is
projected onto display surface 40 by a projection lens 62. The
viewer is provided with a channel differentiator device 230, such
as a pair of polarizing glasses or filter glasses, depending on how
the left and right channels are modulated and provided on display
surface 40.
[0055] FIG. 2 shows the basic model that applies in general for
embodiments of the present invention. Specific embodiments then use
different variations from this model, employing different methods
for differentiating left and right viewing channels, for
conditioning the light provided to each channel, for light
modulation within each channel, for projection of the image onto
display surface 40, and for viewer outfitting to differentiate left
from right channels and to obtain a stereoscopic effect thereby.
Still other alternate embodiments employ the basic arrangement of
FIG. 2 to form a high resolution image that may not be
stereoscopic.
[0056] One option for differentiating left and right channels is to
employ light having different polarization states. Referring to
FIG. 3, there is shown a polarized light providing apparatus 110
that could be used as illumination source 210 in one embodiment,
providing left and right channels of stereoscopic imaging apparatus
200. Light from a light source 20 is uniformized by a uniformizing
element 22 that spatially distributes or homogenizes the light to
provide a more uniform illumination field. The uniformized light is
directed to a shutter 116 and a polarizer 96 that transmits light
having one polarization, such as p-polarization in one embodiment,
to one modulation channel, labeled R for the right channel in FIGS.
2 and 3, as a substantially polarized illumination beam 66.
Polarizer 96 reflects light having the orthogonal polarization
(s-polarization in this example) for the other modulation channel.
A mirror 98, or reflective polarization sensitive coating, then
directs the light having orthogonal polarization to the other
modulation channel, labeled L in FIGS. 2 and 3. Lens 34 directs the
polarized light into the appropriate modulation channel.
[0057] Light source 20 in FIG. 3 can be any of a number of types of
lamp or other emissive component. It can be appreciated that it
would be particularly advantageous to select a commercially
available component as light source 20, to take advantage of low
cost and availability due to high manufacturing volumes. In one
embodiment, a conventional CERMAX.RTM. xenon arc lamp, available
from PerkinElmer Inc., Wellesley, Mass., is used. The capability to
efficiently use the light of such off-the-shelf devices is a
particular advantage when using a larger size TFT LC device, as
opposed to using smaller LCOS components that are unable to use a
significant portion of the light available due to LaGrange
limitations, as noted earlier in the background section. Other
alternative light sources include high-power LEDs, which can be
distributed in an array when using uniformizing optics. Another
option is to use ultra-high pressure Mercury lamps, for example.
Conventional xenon bubble lamps offer yet another option and
provide better color gamut than Mercury lamps. In all of these
cases, substantially unpolarized light is typically provided from
the source.
[0058] In one embodiment, polarizer 96 is a wire grid polarizer,
such as the polarizer type disclosed in U.S. Pat. No. 6,452,724
(Hansen et al.) Wire grid polarizers of various types are
commercially available from Moxtek, Inc., Orem, Utah. The wire grid
type of polarizer is particularly advantaged for handling high
levels of light intensity, unlike conventional types of absorptive
polarizer. In one embodiment the wire grid polarizer is placed such
that wire elements on its wire surface side face toward the LCD
panel. This configuration reduces thermally induced birefringence
as disclosed in commonly assigned U.S. Pat. No. 6,585,378 (Kurtz et
al.) Polarizer 96 could alternately be a conventional prism
polarizer, such as a MacNeille polarizer, familiar to those skilled
in the electronic imaging arts.
[0059] Referring to FIG. 4, there is shown channel modulation
apparatus 220l for the left eye; channel modulation apparatus 220r
for the right eye would be similarly constructed. Here, an LC
modulator panel 60 is segmented into three portions, one for each
component color: Red (R), Green (G), and Blue (B), as is described
subsequently. A condensing lens 38 then directs a uniformized
polarized beam 76 to a color separator 78 that separates the
multiple wavelengths into component color wavelengths,
conventionally red, green, and blue (RGB) along separate
illumination paths 44r (red), 44g (green) and 44b (blue).
[0060] There are at least three component wavelength modulating
sections 114r, 114g, 114b, as shown in FIG. 4, each aligned along a
corresponding illumination path 44r, 44g, 44b. In each component
wavelength modulating section 114r, 114g, 114b, a condensing lens
42r, 42g, 42b directs the corresponding component wavelength
illumination through an optional polarizer 48r, 48g, 48b. Lenses
52r, 52g, and 52b, such as Fresnel lenses, then focus this
illumination through a monochrome transmissive liquid crystal
modulator panel 60 that is segmented to handle each component color
for modulation, as is described subsequently. Liquid crystal
modulator panel 60 forms red, green, and blue component wavelength
beams 54r, 54g, and 54b. Component wavelength beams 54r, 54g, and
54b are the modulated light beams that are combined to form the
color image. Analyzers 56r, 56g, and 56b condition the polarization
of red, green, and blue component wavelength beams 54r, 54g, and
54b. In this embodiment, lenses 61r, 61g, and 61b form image 64 as
an intermediate image for projection. Here, the modulated component
wavelength beams 54r, 54g, and 54b are superimposed to form color
image 64 for projection. It must be noted that image 64 may be an
intermediate image, as described above, or may be the image in the
projection plane.
Configuration of Modulator Panel 60
[0061] One aspect of the present invention relates to the
segmentation of monochrome liquid crystal modulator panel 60, as
shown in the plan view of FIG. 5. The red, green, and blue
component colors in respective red, green, and blue illumination
paths 44r, 44g, and 44b (FIG. 4) are modulated by a red component
modulating section 80r; a green component modulating section 80g,
and a blue component modulating section 80b, respectively. In one
embodiment, where LC modulator panel 60 has 2048.times.3240 pixel
resolution, each component color modulating section 80r, 80g, and
80b has 2048.times.1080 pixel resolution. Higher resolution panel
alternatives would be advantaged for applications such as digital
cinema.
[0062] Each modulating section 80r, 80g, 80b has a corresponding
border portion 82r, 82g, 82b. Border portions 82r, 82g, 82b include
some number of pixels that are unused but available to be used as
part of modulating section 80r, 80g, 80b. Border portions 82r, 82g,
82b are used to facilitate alignment of the component color
modulated light, as is described subsequently.
[0063] Each modulating section 80r, 80g, 80b is separated from its
adjacent modulating section(s) 80r, 80g, 80b by a light blocking
segment 84a, 84b. Light blocking segments 84a, 84b consist of
pixels in a dark or black state, acting as masks for reflecting
overlapping light from adjacent red, green, and blue illumination
paths 44r, 44g, and 44b. Physical blocking elements may be used in
addition to or in lieu of these dark state pixels.
[0064] For the embodiment of FIG. 4, LC modulator panel 60 is
modified and simplified for use in a projection application.
Referring first to FIG. 6A, there is shown a conventional LC
modulator panel 118 as provided by the manufacturer for display
use. In this conventional arrangement, an LC material 120, with its
control electrodes on an ITO layer 124 and thin-film transistors
122 is sandwiched between plates of glass 126, along with a color
filter array 132. Front and rear polarizers 128 are absorptive
sheets whose performance is compromised by high heat levels,
causing variable thermal nonuniformities in the projected image. A
compensation film 130 is also provided for enhancing contrast. In
many devices, other enhancement films are used but not shown, such
as diffusing layers.
[0065] FIG. 6B shows the simplified arrangement of LC modulator
panel 60 as used in the present invention. Compensation film 130
may be removed; even if maintained, the performance requirements
and cost of compensation film 130 are significantly reduced. Front
and rear polarizers 128 are also removed from LC modulator panel 60
itself; separate wire grid polarizers are used for polarizers 48r,
48g, 48b and analyzers 56r, 56g, 56b. Polarizers 48r, 48g, 48b and
analyzers 56r, 56g, 56b are spaced apart from the surface of glass
sheets 126. Wire grid polarizers, capable of handling high light
levels without absorbing substantial amounts of light energy, are
particularly well suited to high intensity application in
stereoscopic display apparatus 200. Spacing them apart from LC
material 120 prevents heat transfer that would negatively impact
the uniformity of the image. Color filter array 132 is no longer
needed. An optional antireflection coating 134, 136 may be provided
on both external surfaces of glass 126. Antireflection coating 134,
136 would help to reduce stray light and increase the ANSI contrast
ratio, minimizing undesirable interactions of light from
neighboring pixels.
Illumination Source and Optics
[0066] A notable improvement over conventional TFT LC projection
apparatus is the use of uniformizing element 22 (FIG. 3) for
providing a uniform illumination from a light source 20.
Uniformizing element 22 conditions the output from light source 20
to provide a uniformly bright illumination beam for modulation. In
one embodiment, an integrating bar provides uniformizing element
22. Alternate embodiments include the use of a lenslet array or
some combination of lenslet and other integrating components.
[0067] An optional shutter 116, whose position may be at the
location of the dotted line in FIG. 3, may be implemented within
polarized light providing apparatus 110 in order to momentarily
darken the display to allow time for a suitable transition between
images. Shutter 116 may be needed depending on LC modulator panel
60 response speed. Although response speeds of LC modulator panels
60 have improved sufficiently for conventional video display, it
remains to be seen if there will be sufficient improvement to allow
imaging with ghost-free motion, particularly with image content
that contains considerable action and transitions. Shutter 116
would be used to block the light to LC modulator panel 60 during
transition times, effectively reducing the overlay of images
between frames. A suitable shutter mechanism is disclosed, for
example, in commonly assigned U.S. Pat. No. 6,513,932 (Ehrne et
al.)
[0068] FIG. 7 shows a perspective view of stereoscopic imaging
apparatus 200 in one embodiment, using the overall arrangement
shown in the schematic block diagram of FIG. 4. Here, individual
modulator panels 601 and 60r are used in left and right channel
modulation apparatus 220l and 220r. Each modulation apparatus 220l
and 220r has a corresponding projection lens 62l and 62r. It must
be observed that other arrangements are possible. For example,
instead of the two modulator panels 60l and 60r shown, a single
modulator panel 60 could be segmented appropriately to provide left
and right viewing channels, such as using a separate color wheel or
color scrolling arrangement for each channel. Optical components
for each channel could cooperate to form a single intermediate
image, thus allowing use of a single projection lens 62 as was
shown in the basic model of FIG. 2. Alternately, there could be a
separate projection lens for each color channel from each channel
modulation apparatus 220l, 220r.
Color Separation
[0069] As was shown in FIG. 4, uniformized polarized beam 76 goes
to color separator 78. In an alternative embodiment, there could be
a separate uniformizer 22 in each channel modulation apparatus
220l, 220r; however, this could cause some non-uniformity between
left- and right-image channels.
[0070] FIG. 8 shows the components of color separator 78 for one
embodiment in more detail. An arrangement of crossed dichroic
surfaces 90a, 90b is used to split the multiple wavelength light of
uniformized polarized beam 76 into the key red, green, and blue
component wavelengths for modulation as red, green, and blue
component wavelength beams 54r, 54g, and 54b, respectively. Turning
mirrors 92 redirect red and blue component wavelength beams 54r and
54b in the embodiment of FIG. 8. Alternate embodiments include use
of dichroic separating components in a fashion such that more than
three color bands are separated, enabling a larger color gamut.
[0071] The improved light efficiency afforded by the use of a large
modulator panel 60 can be utilized to provide a projection gamut
that is substantially larger than that provided using conventional
video, such as SMPTE "C" color space or even proposed Digital
Cinema SMPTE gamut defined by (Red: 0.680 x, 0.320 y, 10.1 Y,
Green: 0.265 x, 0.690 y, 34.6 Y, Blue: 0.150 x, 0.060 y, 3.31 Y).
There is interest in making the gamut at least as large or larger
than that of motion picture film. Dichroic filters can be selected
and positioned to block portions of the spectral bands between the
typical component color bands blue, green, and red, thereby
increasing the color space that stereoscopic imaging apparatus 200
can provide.
Fresnel Lenses
[0072] Use of Fresnel lenses as lenses 52r, 52g, and 52b in
illumination paths 44r, 44g, and 44b, as shown in FIG. 4, is
particularly advantageous for directing light toward the entrance
pupils of corresponding lenses 61r, 61g, and 61b. By placing
Fresnel lenses 52r, 52g, and 52b in illumination paths 44r, 44g,
and 44b, imaging aberrations are minimized. Fresnel lenses are
typically molded and may exhibit nonuniformities that are
particularly visible if the lens is used with image-modulated
light. Of course, other suitable types of lenses could be used for
lenses 52r, 52g, and 52b, preferably lenses with a thin dimensional
profile.
[0073] FIG. 10 shows an alternate embodiment using a pair of lenses
such as Fresnel lenses in each component wavelength modulating
section 114r, 114g, and 114b, one placed as an illumination path
lens in each illumination path 44r, 44g, 44b, the other placed as a
modulated beam lens in each modulated component wavelength beam
54r, 54g, 54b. In the blue color channel, lens 52b is in
illumination path 44b; a second lens 53b is in component wavelength
beam 54b. In the green color channel, lens 52g is in illumination
path 44g; a second lens 53g is in the modulated component
wavelength beam 54g. In the red color channel, lens 52r is in
illumination path 44r; a second lens 53r is in modulated component
wavelength beam 54r. With the arrangement of FIG. 10, first lens
52r, 52g, and 52b in the illumination beam for each component
wavelength modulating section 114r, 114g, 114b reduces the angle of
light directed into modulator panel 60, providing a measure of
collimation, thereby improving the contrast performance. The second
lens 53r, 53g, and 53b would be placed in modulated component
wavelength beam 54r, 54g, 54b from LC modulator panel 60, to direct
the light toward the entrance pupils of corresponding lenses 61r,
61g, and 61b. In one embodiment, each of lenses 52r, 52g, 52b and
53r, 53g, 53b are Fresnel lenses.
[0074] In an alternate embodiment, a pair of crossed cylindrical
Fresnel lenses can be used in one or more of component wavelength
modulating sections 114r, 114g, 114b as an alternative to the
conventional circularly symmetric Fresnel lens types. Crossed
cylindrical Fresnel lenses are rotated with respect to each other
and can be further rotated at an angle to LC modulator panel 60 to
minimize or eliminate moire and aliasing.
[0075] In one embodiment, stereoscopic display apparatus 200 uses
anti-ghost Fresnels, such as those produced by manufacturers such
as Reflexite Corporation, Rochester, N.Y. As another alternative,
holographic optical components could be used in the place of
Fresnel lenses as one or more of lenses 52r, 52g, and 52b. Glass
molded Fresnel lenses would help to minimize problems with stress
birefringence from light absorption, such as decreased contrast
uniformity across the image.
Control Loop for Projection Lens 62 Alignment
[0076] FIG. 9 shows a control loop 100 arranged for automated
alignment, in an embodiment using multiple projection lenses 63r,
63g, and 63b in each color channel. A sensor 104, such as an
electronic camera, senses light from a target 106 that may be part
of image 64 on display surface 40 or may be separated from image
64. Target 106 is devised to show proper overlap of the modulated
component color images projected onto display surface 40. Methods
such as those disclosed in commonly-assigned U.S. Pat. No.
6,793,351 (Nelson et al.) may be used to detect proper overlap at a
control logic processor 108 and to counter any offset between
colors detected by sensor 104. Adjustment of projection lenses 63r,
63g, and 63b may be effected using a combination of methods.
Alignment in units of complete pixels can be accomplished
electronically, by shifting the position of the corresponding red,
green, or blue component modulating sections 80r, 80g, and 80b,
using a method similar to that disclosed in U.S. Pat. No. 5,729,245
(Gove et al.) Corresponding actuators 102r, 102g, and 102b, such as
stepping motors or piezoelectric actuators can be used to effect
fine tuning alignment adjustment, either of full pixels or of
fractional increments of a pixel, by moving projection lenses 63r,
63g, and 63b themselves. In one embodiment, a combination of the
two methods is used, first attempting alignment by shifting the
relative positions of one or more of red, green, or blue component
modulating sections 80r, 80g, and 80b, utilizing pixels in border
portions 82r, 82g, and 82b as needed. Following this shifting of
red, green, or blue component modulating sections 80r, 80g, and
80b, fine tuning adjustment is then performed by driving actuators
102r, 102g, and 102b as needed.
Alternate Embodiments
[0077] The embodiments shown in FIGS. 4, 8, and 9 show stereoscopic
display apparatus 200 using the conventional set of red, green, and
blue component colors. Other arrangements are possible, including
the use of additional colors, to provide an enhanced color gamut.
Or, different component colors could be used to form color image
64. In an alternate embodiment using four colors, two LC modulator
panels 60 could be used in each channel modulation apparatus 220l,
220r, each LC modulator panel 60 configured to have two
component-color modulating sections.
[0078] In an alternate embodiment, a single LC modulator panel 60
is used in combination with a scrolling color filter device that
separates the light into color bands, separated by light blocking
regions. The color bands can be scanned across LC modulator panel
60 using prism optics or using a color wheel or other type of color
scrolling mechanism. A blocking region is utilized to prevent color
blurring during transition times between the colors. The modulator
is subsequently modulated in synchronization with the particular
color light provided to apply the appropriate portion of the
composite color image. Scrolling color background and techniques
are described, for example, in an article entitled "Sequential
Color Recapture and Dynamic Filtering: A Method of Scrolling Color"
by D. Scott Dewald, Steven M. Penn, and Michael Davis in SID 00
Digest, pages 1-4.
[0079] A color scrolling embodiment of stereoscopic imaging
apparatus 200, as shown in FIG. 11, utilizes two modulator panels
60l and 60r, each with a color scrolling element 140l and 140r,
respectively. Color scrolling elements 140l, 140r, such as a color
scrolling wheel or some combination of components including a color
separator with a scanning prism, for example, sequentially scans
color light of various wavelengths using techniques for providing a
spectral profile familiar to those skilled in the digital projector
arts. LC modulator panel 60l, 60r sequentially modulates each
incident color of light provided from color scrolling element 140l,
140r to provide modulated light for projection.
[0080] Each modulator panel 60l, 60r has supporting optical
components in its corresponding illumination path 144l, 144r,
similar to that described with reference to FIG. 4, and provides
modulated light as a component wavelength beam 54c, 54d to a
projection lens 62l, 62r. Illumination optics using color scrolling
components could employ color separation, color scrolling and
light-directing techniques similar to those disclosed in U.S. Pat.
No. 6,280,034 (Brennesholtz), for example.
[0081] Where color scrolling element 140l, or 140r is a color
scrolling wheel, a sequence utilizing repeated complementary pairs
of colors may be particularly advantageous. In such an arrangement,
color scrolling element 140l, providing a spectral profile for the
left-eye image, could be a filter wheel having a red, green, and
blue filter for forming its set of colors. Color scrolling element
140r, providing a different spectral profile for the right-eye
image, would then be a filter wheel having complementary cyan,
magenta, and yellow filter for forming its set of colors. The
sequencing of these filter wheels would be timed so that the
combined image formed from the two modulator panels 60l, 60r would
be additive with respect to color, with the combined image
appearing to be white during each part of the scrolling sequence.
This would be the case, for example, when simultaneously projecting
each primary color (red, green, blue) paired with its corresponding
complement color (cyan, magenta, yellow). Combining this approach
with the advantages of enhanced brightness and improved imaging
performance provided by the present invention allows an expanded
color gamut over earlier designs.
[0082] In an alternate embodiment, instead of providing two
separate modulator panels 60l, 60r, a single modulator panel 60
could be subdivided into two segments. One segment would serve for
the right channel, the other for the left.
[0083] Images from either two color wheels or from channels using
three color component wavelength modulating sections 114r, 114g,
and 114b can be combined at an intermediate image plane. With this
arrangement, intermediate image 64 may actually be smaller than
modulator panel 60, so that intermediate image 64 can be magnified
to the large screen size by a single projection lens 62. Optical
convergence can be done at the time of fabrication, so that only a
single projection lens adjustment is necessary for an operator.
This approach has been shown to be of value as demonstrated in
commonly assigned U.S. Pat. Nos. 6,808,269 (Cobb) and U.S. Pat. No.
6,676,260 (Cobb et al.)
[0084] Referring again to FIG. 10, there is shown a block diagram
of stereoscopic imaging apparatus 200 in an alternate embodiment
using individual red, green, and blue light sources 46r, 46g, and
46b in an illumination section 68. Light sources 46r, 46g, and 46b
may include lasers, LEDs, or other light source types and may also
be supported by light conditioning components such as uniformizers,
as were described with reference to FIG. 3. Light sources 46r, 46g,
and 46g may be polarized or provided with polarizers.
[0085] One advantage of the present invention is that compensators
may not be needed or at least that the need for compensators may be
minimized. As is well known in the art, there are two basic types
of compensator films. An uniaxial film with its optic axis parallel
to the plane of the film is called an A-plate. An uniaxial film
with its optic axis perpendicular to the plane of the film is
called a C-plate. Alternately, the A-plate can be described as
providing XY birefringence (an anisotropic medium with XY
retardance) in the plane of the compensator, while the C-plate
provides Z birefringence along the optical axis in the direction of
beam propagation through the compensator. A uniaxial material with
n.sub.e greater than n.sub.o is called positively birefringent.
Likewise, a uniaxial material with n.sub.e smaller than n.sub.o is
called negatively birefringent. Both A-plates and C-plates can be
positive or negative depending on their n.sub.e and n.sub.o values.
As is well known in art, C-plates can be fabricated by the use of
uniaxially compressed polymers or casting cellulose acetate, while
A-plates can be made by stretched polymer films such as polyvinyl
alcohol or polycarbonate.
[0086] The present invention minimizes or eliminates the need for
C-plate compensators, since using the larger LC panels as modulator
panel 60 results in reduced angular sensitivity. Referring to FIG.
4, a dotted line 142 indicates a possible position for an optional
A-plate compensator in red component wavelength beam 54r. Other
component wavelength modulating sections 114r, 114g, and 114b may
also benefit from an A-plate compensator in a similar position.
Alternately, a compensator could be disposed in the illumination
path, such as prior to Fresnel lens 52r, 52g, 52b, for example. In
other embodiments, A-plate compensation may be supplemented with
some additional level of C-plate compensation. In still other
embodiments, a C-plate compensator would be sufficient. Any of a
number of types of compensator can be used, including film based
compensators, compensators formed from a multilayer thin film
dielectric stack, and compensators using formed birefringent
structures, for example.
[0087] In an alternate embodiment, as shown in the block diagram of
a portion of a projection apparatus in FIG. 12, shown in
perspective for clarity, a polarization beamsplitter 148r, 148g,
148b is provided as an analyzer for each modulated component
wavelength beam 54r, 54g, 54b from modulator panel 60. Polarization
beamsplitters 148r, 148g, 148b, wire grid polarization
beamsplitters in one embodiment, turn the optical path of each
component wavelength beam 54r, 54g, 54b. In the embodiment of FIG.
12, projection lenses 62r, 62g, and 62b then form an image on
display surface 40. In another alternate embodiment, an
intermediate image could be formed, as was described above.
[0088] Referring to FIG. 13, there is shown a schematic block
diagram of an alternate embodiment in which modulated light from
each color channel is directed by lens 63r, 63g, 63b to a V-prism
assembly 150. V-prism assembly 150 combines the modulated light
onto a single optical path for forming an intermediate image 146 at
the pupil of projection lens 62. V-prism assembly 150 is one type
of color combiner using dichroic surfaces and working in
combination with mirrors 152 to direct light toward projection lens
62. Commonly-assigned U.S. Pat. No. 6,676,260 (Cobb et al.)
describes V-prism use in projection apparatus.
[0089] Where polarization beamsplitters 148r, 148g, 148b in FIG. 12
are wire grid polarization beamsplitters, such as those provided by
Moxtek, Inc., rotation of one of these devices about the optical
axis can be used to provide a measure of compensation, using
methods disclosed in commonly-assigned U.S. Pat. No. 6,805,445
(Silverstein et al.)
[0090] By comparison with conventional electronic display devices,
stereoscopic imaging apparatus 200 of the present invention
provides high brightness levels. Where spatial light modulators
30r, 30g, and 30b of the conventional arrangement in FIG. 1 are
miniaturized LCOS LC devices, the LaGrange invariant and
energy-carrying capacity of these devices constrains the amount of
brightness that is available to a range from about 5,000 to no more
than about 25,000 lumens. In contrast, the embodiment of FIG. 4
enjoys an expanded luminance range, allowing projection in excess
of 30,000 lumens per channel.
[0091] The dimensions of LC modulator panel 60 can be optimized to
suit the performance requirements of stereoscopic imaging apparatus
200. In contrast to the miniaturized LCOS LCD solutions previously
used, LC modulator panel 60 can be a large scale device larger than
typical laptop displays, up to 17-20 diagonal inches or more.
Although early LC panels were disappointingly slow, ongoing work
has provided speed improvements of 100% and better and it appears
that increased speeds are feasible. Improved response times of 8
msec or shorter have been reported. Ideally, modulator panel 60 can
be sized just big enough such that the full lamp system efficiency
can be utilized and small enough to give the fastest response time,
with the optimum size for pixel structure and electronics to be
fabricated utilizing standard TFT panel methods. Preferably, liquid
crystal modulator panel 60 has at least a minimum diagonal of 5
inches. This larger size helps to maximize light throughput and to
maximize resolution of the displayed image.
[0092] Sizing a TFT panel to be best suited to the lamp system
efficiency involves a number of considerations. For example, to
utilize a Cermax style lamp with a 2.0 mm arc gap, measurements
show that the full efficiency of the lamp can be captured by a
system having a LaGrange invariant, defined as the product of the
numerical aperture times the diagonal of the modulator area, of
approximately 10. A system designed at f/10.0 has numerical
aperture (NA) equal to 0.05. Thus, the device diagonal would need
to be 200 mm. This value would need to be doubled in order to
capture both polarization states. Additionally this modulation area
would be required for each wavelength band chosen. Thus, from a
system efficiency standpoint, a panel that is slightly larger than
1074.times.358 mm would be very efficient and offer the best
potential for fast transition times. The main difficulty would be
to fabricate pixel electronics to be small enough to accommodate
this size at the high resolutions desired: 2048.times.1024 or
4096.times.2048 for each wavelength band modulated. The preferred
embodiment of the stereoscopic imaging apparatus 200 can be made
such that each orthogonal polarization state can be placed on
separate modulator panels 60 fabricated to this optimal size.
[0093] With its capability for using brighter light sources and use
of a large-area image generator, stereoscopic imaging apparatus 200
using TFT LC modulator panel 60 as in FIG. 4 offers an overall
efficiency on the order of 40-50%. This is in contrast to the
typical efficiency of earlier LCOS LCD designs of FIG. 1, where
efficiencies of no more than about 5 to 10% are common. Wire grid
polarizers are particularly advantageous, since they exhibit
relatively low light absorption. In general, a polarizer having
light absorption of less than about 20% would be preferred. There
may also be improved performance obtained by orienting the wire
grid surface itself toward modulator panel 60 in the embodiments
described above.
[0094] With stereoscopic imaging apparatus 200, as well as with any
imaging apparatus that employs TFT LC modulator panels 60, there
may be a need to increase the apparent resolution of output pixels
in the image that is displayed or to compensate for edge effects
between pixels. Referring to FIGS. 14 and 15, there are shown two
different solutions for addressing this problem, not only for
stereoscopic imaging apparatus 200, but also for any type of
imaging apparatus 50 that uses more than one LC modulator panel 60.
In FIG. 14, imaging apparatus 50 uses dithering to improve pixel
fill factor and improve the apparent resolution of LC modulator
panels 60l and 60r. Each LC modulator panel 60l and 60r is
mechanically coupled to an actuator 160 that provides dither
motion. FIG. 15 shows another alternative, using blur filters 162,
shown in dotted lines, for modulated light output from LC modulator
panels 60l and 60r.
[0095] Stereoscopic imaging apparatus 200 in the embodiments of
FIGS. 14 and 15 can provide twice the pixel count of a non
stereoscopic imaging system. The arrangement of FIGS. 14 and 15 can
even be used for non stereoscopic image display. For example, with
respect to FIG. 14, it is possible to dither one or more of TFT LC
modulator panels 60l, 60r with respect to each other in order to
effectively provide a higher resolution image to the viewer. The
relative position of the pixels and pixel overlap can be
conditioned along with the time period of viewing and the response
time of the eye to minimize artifacts due to interpixel gaps and to
provide higher display resolution. A feedback control loop, such as
that described with reference to FIG. 9, could alternately be
employed to monitor and correct for dithering problems.
[0096] Another alternate embodiment of stereoscopic imaging system
200 is shown in FIG. 16. Here, a switchable polarization rotating
element 70 is employed to switch polarization states rapidly,
alternating between left- and right-eye polarization states at
sufficient speed in cooperation with images formed on modulator
panel 60 that, in turn, cooperates with color scrolling element
140. A half-wave plate 72 is used to change the polarization state
of a portion of the light from light providing apparatus 110. For
example, an electrically induced retarder, such as a switchable
liquid crystal retarder could be used as switchable polarization
rotating element 70. Alternately, a rotating half-wave plate could
be used. Of course, for this embodiment, switching times of
modulator panel 60 must be fast enough for eye response. This same
type of polarization switching could provide alternating left- and
right-eye images for stereoscopic viewing when used with other
light modulation arrangements as well as with color scrolling
element 140. For example, with reference back to FIG. 4, a single
modulator panel 60 and color separator 78, such as the dichroic
color separator shown, could be used to provide stereoscopic
imaging with polarization rotating element 70, added at or near the
position of image 64. Thus, the modulation components shown as left
channel modulation apparatus 2201 in FIG. 4 could be easily
adapted, with the addition of polarization rotating element 70 at
or near the position of image 64, for alternately providing left-
and right-eye images to a viewer. The embodiment of imaging
apparatus 50 in FIG. 10, with an individual light source 46r, 46g,
or 46b for each color channel, could also be adapted for
stereoscopic viewing in a similar manner, with the addition of
polarization rotating element 70 at or near the position of image
64.
[0097] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention as described above, and as noted in the
appended claims, by a person of ordinary skill in the art without
departing from the scope of the invention. For example, the
embodiments described hereinabove can be used to form an
intermediate image or to provide color modulated beams that are
separately projected onto display surface 40. Alternative types of
more recently introduced TFT components are possible, including
organic thin-film transistors (OTFTs) based on conjugated polymers,
oligomers, or other molecules and thin film transistors utilizing
monolayers of well-dispersed single wall carbon nanotubes.
[0098] Thus, what is provided is an apparatus and method for a
stereoscopic display apparatus using one or more TFT LC panels for
forming the displayed image.
PARTS LIST
[0099] 10 projection apparatus [0100] 20 light source [0101] 20r
light source, red [0102] 20g light source, green [0103] 20b light
source, blue [0104] 22 uniformizing element [0105] 22r uniformizing
element, red [0106] 22g uniformizing element, green [0107] 22b
uniformizing element, blue [0108] 24r polarizing beamsplitter, red
[0109] 24g polarizing beamsplitter, green [0110] 24b polarizing
beamsplitter, blue [0111] 26 dichroic combiner [0112] 30r spatial
light modulator, red [0113] 30g spatial light modulator, green
[0114] 30b spatial light modulator, blue [0115] 32 projection lens
[0116] 34 lens [0117] 38 lens [0118] 40 display surface [0119] 42r
condensing lens, red [0120] 42g condensing lens, green [0121] 42b
condensing lens, blue [0122] 44r illumination path, red [0123] 44g
illumination path, green [0124] 44b illumination path, blue [0125]
46r light source, red [0126] 46g light source, green [0127] 46b
light source, blue [0128] 48r polarizer, red [0129] 48g polarizer,
green [0130] 48b polarizer, blue [0131] 50 imaging apparatus [0132]
52r Fresnel lens, red [0133] 52g Fresnel lens, green [0134] 52b
Fresnel lens, blue [0135] 53r Fresnel lens, red [0136] 53g Fresnel
lens, green [0137] 53b Fresnel lens, blue [0138] 54c component
wavelength beam [0139] 54d component wavelength beam [0140] 54r
component wavelength beam, red [0141] 54g component wavelength
beam, green [0142] 54b component wavelength beam, blue [0143] 56r
analyzer, red [0144] 56g analyzer, green [0145] 56b analyzer, blue
[0146] 60 modulator panel [0147] 60l modulator panel [0148] 60r
modulator panel [0149] 61r lens, red [0150] 61g lens, green [0151]
61b lens, blue [0152] 62 projection lens [0153] 62l projection lens
[0154] 62r projection lens [0155] 63r lens, red [0156] 63g lens,
green [0157] 63b lens, blue [0158] 64 image [0159] 66 polarized
illumination beam [0160] 68 illumination section [0161] 70
switchable polarization rotating element [0162] 72 half-wave plate
[0163] 76 uniformized polarized beam [0164] 78 color separator
[0165] 80r red component modulating section [0166] 80g green
component modulating section [0167] 80b blue component modulating
section [0168] 82r border portion, red [0169] 82g border portion,
green [0170] 82b border portion, blue [0171] 84a light blocking
segment [0172] 84b light blocking segment [0173] 90a dichroic
surface [0174] 90b dichroic surface [0175] 92 turning mirror [0176]
96 polarizer [0177] 98 mirror [0178] 100 control loop [0179] 102r
actuator, red [0180] 102g actuator, green [0181] 102b actuator,
blue [0182] 104 sensor [0183] 106 target [0184] 108 control logic
processor [0185] 110 polarized light providing apparatus [0186]
114r component wavelength modulating section, red [0187] 114g
component wavelength modulating section, green [0188] 114b
component wavelength modulating section, blue [0189] 116 shutter
[0190] 118 LC modulator panel [0191] 120 LC material [0192] 122
thin-film transistor (TFT) [0193] 124 ITO layer [0194] 126 glass
[0195] 128 polarizer [0196] 130 compensation film [0197] 132 color
filter array [0198] 134 antireflection coating [0199] 136
antireflection coating [0200] 140 color scrolling element [0201]
140l color scrolling element [0202] 140r color scrolling element
[0203] 142 line [0204] 144l illumination path [0205] 144r
illumination path [0206] 146 intermediate image [0207] 148
polarization beamsplitter [0208] 148r polarization beamsplitter,
red [0209] 148g polarization beamsplitter, green [0210] 148b
polarization beamsplitter, blue [0211] 150 V-prism assembly [0212]
152 mirror [0213] 162 blur filter [0214] 200 stereoscopic imaging
apparatus [0215] 210 illumination source [0216] 220l channel
modulation apparatus [0217] 220r channel modulation apparatus
[0218] 230 channel differentiator device
* * * * *